The Ericsson MC218 is "almost" the same as Psion 5. But the problem is in "almost". Ericsson has changed a few bits for own gain in order to sell Ericsson's stuff which never made it. I don't know any more if that was with connecting.
See to it that you have the right com port and set to the right baud on the MC218 and on the OS machine. Read the file PsionPlugin_doc.htm and verify it with the command files. It might be that the MC can't handle 115200 baud, try one step lower. If problem stays, check your cable. You can take the cable and test each pen with an Ohm meter. It should read almost 0 Ohm if it has a connection or infinitive without connection.
That's all I can do for you, if you had series 3, then it would be different. Succes.